A sample of methane gas, CH4 was collected over water at 25 degrees celcius and 720 torr. The volume of the wet gas is 2.50L. What will be the volume of the dry methane at a standard pressure?

Answer 1

I would use
(P1V1/T1) = (P2V2/T2)and solve for V2.
For P1, use 720 torr minus vapor pressure H2O at 25 degrees C. You can find that in tables; it varies with T and is approximately 25 torr at 25 C but you need to use the value in the table.